The Unknown Eruption

“We are, all of us, growing volcanoes that approach the hour of their eruption; but how near or distant that is, nobody knows—not even God.” —Friedrich Nietzsche

In A Nutshell

The early 1800s were unusually cold, with crops destroyed and people starving because of an unseasonal frost. In fact, 1816 was dubbed the “Year Without Summer” and, in a reflection of how many people lacked food, the “Year of the Beggar.” Researchers believed that two huge volcanic eruptions were to blame by blacking out the Sun. The second one, the 1815 Tambora volcanic eruption, was well known, but scientists struggled to find evidence and details of the first one six years earlier. In addition to markers in Antarctica and Greenland, scientists have finally found eyewitness accounts of the unknown eruption.

The Whole Bushel

In the last 500 years, the coldest decade recorded was 1810 to 1819. Those years were abnormally cold, with crops destroyed and people starving because of an unseasonal frost. In fact, 1816 was dubbed the “Year Without Summer” and, in a reflection of how many people lacked food, the “Year of the Beggar.”

Researchers believed that two huge volcanic eruptions were to blame by blacking out the Sun with soot and smoke. The second event, the huge 1815 Tambora volcanic eruption in Indonesia that killed almost 90,000 people, was well known. But that didn’t explain the cold years before 1815, which led scientists to believe that another smaller eruption had occurred earlier in the decade.

Immense volcanic eruptions cause global cooling, sometimes for years, by releasing sulfur gases into the stratosphere, Earth’s second atmospheric layer approximately 10–50 kilometers (6–30 mi) above the planet surface. From there, the gases may spread around the world. If the sulfur gas doesn’t reach the stratosphere, then effects on the weather will remain local.

In the 1990s, scientists finally found the physical proof they needed to confirm that a volcanic eruption, dubbed the “unknown eruption,” had occurred in 1809. It got its name because no one from that time period had seemed to take notice of the event. Researchers weren’t sure exactly where or when it had occurred. But chemical markers in ice from Greenland and Antarctica clearly recorded a violent eruption that impacted the stratosphere. Ice sheets in those areas record events in the Earth’s atmosphere, in this case showing massive amount of volcanic sulfuric acid that corresponded to 1809 and 1810. It’s those sulfuric acids in aerosol form that block the Sun and reduce the Earth’s temperature.

“We’ve never seen any evidence of this eruption in Greenland that corresponds to a simultaneous explosion recorded in Antarctica before in the glacial record,” said Mark Thiemens, Dean of the Division of Physical Sciences at UC San Diego. “But if you look at the size of the signal we found in the ice cores, it had to be huge. It was bigger than the 1991 eruption of Mount Pinatubo in the Philippines, which killed hundreds of people and affected climate around the world.”

Altogether, the evidence points to a single, massive volcanic eruption in 1809 which, combined with the Tambora eruption, produced the coldest decade on record in five centuries. Tambora spewed around 100 million tons of sulfur gas into the stratosphere. Based on samples from the Greenland and Antarctic ice sheets, the unknown eruption was about half as big. However, the appearance of sulfuric acid in both polar regions suggests that the unknown eruption probably happened in the tropics. That would allow the wind to carry the resulting soot and smoke throughout the world.

However, researchers were puzzled by the apparent lack of references to the unknown eruption in historical accounts. Having pinpointed the eruption to 1809, they began their search of the archives around that time and finally found descriptions of the event from a scientist and a physician located on different sides of the equator. The scientist in Colombia described a transparent cloud in the stratosphere that changed the Sun’s color to a Moon-like silver. At the same time, the physician in Peru wrote of sunset afterglows, which are caused by sulfuric acid aerosols in the stratosphere. These two eyewitness accounts suggest that the unknown eruption happened within two weeks of December 4, 1808.